git-commit-vandalism/Documentation/technical/api-builtin.txt
Junio C Hamano 530e741c72 Start preparing the API documents.
Most of them are still stubs, but the procedure to build the HTML
documentation, maintaining the index and installing the end product are
there.

I placed names of people who are likely to know the most about the topic
in the stub files, so that volunteers will know whom to ask questions as
needed.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-12-14 22:29:38 -08:00

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builtin API
===========
Adding a new built-in
---------------------
There are 4 things to do to add a bulit-in command implementation to
git:
. Define the implementation of the built-in command `foo` with
signature:
int cmd_foo(int argc, const char **argv, const char *prefix);
. Add the external declaration for the function to `builtin.h`.
. Add the command to `commands[]` table in `handle_internal_command()`,
defined in `git.c`. The entry should look like:
{ "foo", cmd_foo, <options> },
where options is the bitwise-or of:
`RUN_SETUP`::
Make sure there is a git directory to work on, and if there is a
work tree, chdir to the top of it if the command was invoked
in a subdirectory. If there is no work tree, no chdir() is
done.
`USE_PAGER`::
If the standard output is connected to a tty, spawn a pager and
feed our output to it.
. Add `builtin-foo.o` to `BUILTIN_OBJS` in `Makefile`.
Additionally, if `foo` is a new command, there are 3 more things to do:
. Add tests to `t/` directory.
. Write documentation in `Documentation/git-foo.txt`.
. Add an entry for `git-foo` to the list at the end of
`Documentation/cmd-list.perl`.
How a built-in is called
------------------------
The implementation `cmd_foo()` takes three parameters, `argc`, `argv,
and `prefix`. The first two are similar to what `main()` of a
standalone command would be called with.
When `RUN_SETUP` is specified in the `commands[]` table, and when you
were started from a subdirectory of the work tree, `cmd_foo()` is called
after chdir(2) to the top of the work tree, and `prefix` gets the path
to the subdirectory the command started from. This allows you to
convert a user-supplied pathname (typically relative to that directory)
to a pathname relative to the top of the work tree.
The return value from `cmd_foo()` becomes the exit status of the
command.